Transposition

Transposition is the process by which two differing orders of play lead to the same position. In Go, this occurs relatively rarely, but there are some occasions on which it is possible, particularly in the opening.

Transposition is not to be confused with mirror symmetry or point symmetry (mane, or mirror, go.)

The branching of variations of lines of play form structures that are called trees in mathematics (graph theory) and computer science, and increasingly in common parlance. When two branches grow together, the structure is called a Directed Acyclic Graph (DAG). The best SGF editors (such as CGoban2, gGo, etcetera) handle graphs very well, but do not handle DAGs at all.

Confused: A DAG capable editor would bring you back to the main line (or another line) if a variation ends in a position that is already present in that line. This would be a cool feature to show, that both variations leads to the same end and the continuations from there are identical.